1. Field of the Invention
The present invention relates generally to a system for leak detection in storage tanks. More specifically, the present invention relates to a portable rapid test leak detection system for accurate and reliable leak detection in underground storage tanks which have a fuel storage capacity of between 50,000 gallons and 100,000 gallons.
2. Description of the Prior Art
In 1988, Environmental Protection Agency issued to the States Underground Storage Tank (UST) regulations for fuel storage. The UST regulations were issued to implement monthly monitoring and annual tightness testing of the USTs. Monthly monitoring of USTs requires that a leak detection system be certified to detect a leak rate of 0.2 gallons per hour (GPH) and annual tightness testing requires a certification to detect a leak rate of 0.1 GPH. Each certification requires a probability of detection of at least 95% and a probability of false alarm of no more than 5%.
The Department of the Navy owns and operates approximately 1267 underground storage tanks that have a storage capacity of less than 100,000 gallons. These tanks, commonly operating at base fuel farms, must comply with EPA, state, and local regulations and require that either an annual tightness test with monthly inventory reconciliation or monthly monitoring tests be conducted in accordance with published performance standards. Existing technologies either cannot meet performance standards for the large 50,000 to 100,000 gallon USTs or do not provide for a cost-effective solution to mandatory leak detection testing.
One leak detection method used in the past to detect leaks is the tracer method. The tracer method injects a UST with a known tracer chemical and takes samples from monitoring wells placed around the UST. If the tracer chemical is found in the monitoring well samples, the tank is declared to be leaking. There are however technical problems associated with this method of leak detection. For example, certain geologic and groundwater conditions exclude the tracer method's use at particular sites. Also, the cost of the tracer method is very expensive due to recurring sampling and analysis costs.
A wide variety of technologies are utilized to meet monthly and annual leak detection requirements of gasoline stations, which normally use storage tanks that have a storage capacity of 10,000 gallons, or less. In tank detectors are one of the most common leak detection systems for gasoline stations. However these systems, which are certified for 10,000 gallon tanks, do not meet performance standards for the 50,000 to 100,000 gallon tanks.
Bulk fuel tank leak detection systems, which are designed to detect leaks in USTs containing several million gallons of fuel, do have the technical capability to meet performance standards for 50,000 to 100,000 gallon tanks. However, bulk leak detection systems are very expensive, heavy, usually non-portable, can be very slow to stabilize, and may require rigorous operator input and analysis.
Statistical Inventory Reconciliation (SIR) is another common method of UST leak detection. However, this method is very labor intensive in that is requires daily hands-on monitoring. This method does not work well for tanks having a low frequency of fuel transfers (typical of larger tanks), and cannot detect leaks in real time.